1. Field of the Invention
The present invention relates to perpendicular magnetic recording heads that allow control of the amount of float with a read part that can be thermally expanded to protrude locally toward a recording medium.
2. Description of the Related Art
Perpendicular recording, in which a recording medium is magnetized in a direction perpendicular to a surface thereof, has been expected to support achievement of higher recording densities in future because this system enables recording of magnetic information at higher densities than longitudinal recording, in which a recording medium is magnetized in a direction parallel to a surface thereof. A thin-film magnetic head utilizing perpendicular recording (perpendicular magnetic recording head) includes a read part for reading magnetic recording information from a recording medium by a magnetoresistance effect and a write part, disposed above the read part, for recording magnetic information on the recording medium by applying a recording magnetic field perpendicular thereto (perpendicular magnetic field). The read part includes, for example, opposing lower and upper shield layers separated by a predetermined distance in a surface of the head facing the recording medium and a multilayer film disposed between the lower and upper shield layers to provide a magnetoresistance effect. The write part includes, for example, a main pole layer, a return yoke layer disposed opposite the main pole layer with a magnetic gap layer disposed therebetween in the surface facing the recording medium, and a write coil disposed between the main pole layer and the return yoke layer to apply a recording magnetic field to the main pole layer.
A minimal distance between the perpendicular magnetic recording head and the recording medium (amount of float) is preferred to enhance head characteristics (particularly, read characteristics). A variety of magnetic recording heads have been proposed which include a heating element capable of generating heat when supplied with current near a read part so that the read part can be thermally expanded to protrude toward the recording medium by about several nanometers. The heating element is formed between any layers constituting the element parts in a flat pattern parallel to the surfaces of the layers. For example, the heating element can be disposed in the same layer as the read part behind the read part in a height direction, above a return yoke layer, or between the read part and the write part.
Known perpendicular magnetic recording heads are disclosed in, for example, Japanese Unexamined Patent Application Publication Nos. 2003-297029 and 2006-134461 and U.S. Patent Application Publication Nos. US20040130820 A1 and US20050083608 A1.
If, however, a heating element is disposed between a write part and a read part, heat is transferred from the heating element to a write coil to promote a rise in coil temperature. FIG. 5 is a graph showing measurements of the temperature rise (° C.) of write coils of perpendicular and longitudinal thin-film magnetic recording heads with varying powers (mW) supplied to heating elements. FIG. 5 shows that the write coil of the perpendicular magnetic recording head experiences a larger temperature rise than that of the longitudinal magnetic recording head and that the difference in temperature rise is increased as the power supplied to the heating elements is increased. As the coil temperature rises, heat is concentrated into a main pole layer disposed above the write coil. As a result, the main pole layer is thermally expanded to protrude toward a recording medium. If the amount of protrusion of the main pole layer is larger than that of the read part, the main pole layer comes into contact with the recording medium before the read part does. This can result in degraded read/write characteristics and damage to the recording medium.